X-ray apparatus and method of construction

ABSTRACT

554,545. Copper -containing solder alloys. BRITISH THOMSON - HOUSTON CO., Ltd., (General Electric Co.). June 16, 1942, No. 8247. Drawings to Specification. [Class 82 (i)] [Also in Groups XXII and XL] In soldering or brazing beryllium to steel or other metals such as in forming a vacuum-tight joint between a beryllium window and the body of an X-ray apparatus for examining chemical substances &amp;c. an alloy is used of a metal which goes into solution relatively slowly with beryllium when both metals are in the molten state. The alloy has a melting point above 700‹C and preferably between 700‹C and 900‹C and may consist of equal parts of copper and silver and brazing may be effected in a hydrogen furnace with calcium chloride as a flux. Another alloy may consist of 80 per cent of copper, 15 per cent of nickel and 5 per cent of iron which has a melting point about 1200 ‹C.

Feb. 9, 1943. 2. J. ATLEE ETAL X-RAY APPARATUS AND METHOD OFCONSTRUCTION Filed Jan. 8, 1941 3 g Mg J M Patented Feb. 9, 1943 X-RAYAPPARATUS AND METHOD OF CONSTRUCTION Zed J. Atlee, Elmhurst,

Evanston,

and Howard Brackney,

111., assignors to General Electric X-Bay Corporation, Chicago, Ill., acorporation of New York Application January 8, 1941, Serial No. 373,630

Claims.

This invention relates to a new and improved type of X-ray apparatus andto a new and improved method for the construction of such an apparatus.

An important object of the invention is to produce a new and improvedtype of evacuated tube, more particularly an X-ray generator, in whichthe outer casing of the tube is constructed in such a manner as topermit the maximum passage of X-rays therethrough.

Another object of the invention is to provide a new and improved type ofX-ray generator which is particularly well suited for making X-raydiffraction patterns of chemical substances, or other material.

Another object of the invention is to provide a new and improved type ofevacuated tube, more particularly an X-ray generator, in which thewindow through which the X-rays pass is constructed of beryllium and isdisposed in the outer casing of the tube.

Another important object of the invention is to provide a new andimproved method for brazing or soldering beryllium to other metals.

Still another important object of the invention is to provide a new andimproved method for producing a vacuum-tight joint between beryllium andanother metal in an evacuated tube such as an X-ray generator, wherebythe X-rays generated may be passed directly through the beryllium windowwithout passing through any intermediate material which might tend toabsorb them.

Still a further object of the invention is to produce an X-ray tubeespecially suitable for making X-ray difiraction patterns andcharacterized particularly by the fact that greater intensity andconcentration of the X-ray on the substance to be examined can beobtained.

Still an additional object of the invention is to provide a new andimproved type of X-ray generator having a window constructed ofberyllium with a minimum amount of absorption of X-rays of the K-alphaline.

Another important object of the invention is to provide a means forforming a vacuum-tight joint between beryllium and another metal in theouter casing of an evacuated envelope by employing a solder or brazingcomposition comprising a combination of a metal which has a tendency togo into solution with beryllium very rapidly with another metal thatgoes into solution with beryllium very slowly.

These and numerous other important objects,

advantages, and inherent functions of the invention will become apparentas the same is more fully understood from the following description,which, taken in connection with the accompanying drawing, discloses apreferred embodiment of the invention.

Referring to the drawing:

Figure 1 represents a sectional view taken through an X-ray generator ofa type con structed in accordance with the present invention;

Figure 2 is a plan view of one end of the X-ray generator of Figure 1with which-the present invention is especially concerned; and

Figure 3 is an enlarged cross-sectional view taken along the line 3-3 ofFigure 2.

As shown by the drawing, the present invention may be illustrated by anX-ray generator I I comprising an anode or target l3 made of copper orother suitable material, such as iron, molybdenum, cobalt, chromium, ornickel cast in copper, and supported within a sealed envelope l5comprising a hard glass portion l1 and a metal portion [9 constructed ofcold rolled steel or other suitable material.

Any suitable means may be employed for generating the cathode rayutilized in bombarding the target l3. Thus, in the particular embodimentshown, a line focus cathode 2| is employed, which is furnished with asource of electrical energy through conductors 23 and 25. A conductor 21is provided in order to supply electrical energy to a getter wire 29.All conductors are introduced into the evacuated portion of the envelopethrough vacuum-tight joints, such as shown by the joints 3|, 33 and 35.Since the tube is immersed in an oil bath, the oil circulating throughthe area 31 serves to cool the cathode portion oi the tube. As shown,the cathode 2| is surrounded by a shield 39.

The cathode rays R, impinging on the target [3, generate the X-rays X,which pass through a small port 4| and then through a vacuum-tightberyllium window pane or plate which is brazed or soldered to thesurrounding metal 45 by means of a special type of alloy indicated at41. The useful beam of 'the X-ray, passing through port 4| and berylliumwindow pane or plate 43, is preferably taken off at an angle of aboutfour to eight degrees relative to the target l3 As shown in Figure 2,the port 4| is preferably oblong or elliptical in cross-sectional shape.The target I3 is cooled by a direct connection to tap water or othersuitable source of water or other cooling fluid, which is introducedthrough a conduit 49 circulated through the anode cooling chamber 5! andremoved through the outlet conduit 53 The invention herein described isparticularly concerned with the beryllium window 43 and the means forattaching it to member 45 in order to produce a vacuum-tight berylliumwindow Joint. It has been found, in accordance with this invention, thatan alloy of a metal which has a tendency to form solutions withberyllium rapidly, and a metal which has a tendency to form solutionswith beryllium very slowly, can be employed in order to solder or form avacuumtight joint between beryllium and other metals, as, for example,cold rolled steel.

In accordance with a preferred embodiment of the invention, we havefound that a special alloy, containing about 50% silver and about 50%copper, will form a vacuum-tight joint between a beryllium plate and asteel bushing when the brazing is done in a hydrogen furnace and calciumchloride is used as a flux. This particular alloy, which represents apreferred embodiment of the invention, has the necessary .properties ofwetting the beryllium but yet not going into full solution with itbefore a satisfactory joint is formed. In order that an alloy may fiowevenly over the surface of the beryllium to form a joint, it must be ina highly molten state. But the higher the temperature, the faster is therate at which beryllium will go into solution with metals or alloys withwhich it has any tendency at all to form solutions. For example, purecopper, in the molten state, goes into solution very rapidly withberyllium. On the other hand, pure silver, in the molten state, goesinto solution with beryllium very slowly. Alloys of copper and silverhave intermediate rates of solution. Moreover, all alloys of copper andsilver have melting points lower than that of pure copper. All alloyshaving less than about of copper have melting points lower than that ofpure silver. Therefore, alloys of copper and silver have the addedadvantage that they can be used at lower temperatures, which possibilityadds further to the control of the rate of solution with beryllium. Forthe purpose of the present invention it is preferable that the relativeamounts of copper present in the alloy of copper and silver be greaterthan the relative amount of copper present in its eutectic composition.The eutectic composition consists of 72% silver and 28% copper.

In actual practice, the vacuum-tight joints which are obtained with thealloy containing 50% silver and 50% copper go into solution over thewelded or soldered portions of the surface of the beryllium plate to adepth of only a few thousandths of an inch.

The thickness of the beryllium plate 43 may vary, but good results havebeen obtained by employing a plate having a thickness from about a: toabout 1 5 of an inch. It will be understood, of course, that theinvention is not limited specifically to the use of alloys of silver andcopper containing 50% of each ingredient, nor is it specifically limitedto silver or copper alloys, although it is preferable, for the purposeof the present invention, that the alloy be one which is molten at atemperature within the range from 700 C. to 900 C.

In making vacuum tubes, and particularly in making X-ray generators, theuse of alloys for brazing which have a melting point greater than about900 C. is undesirable because of the possibility of cracking or checkingparts of the tube, and also because the higher the temperature, thegreater is the possibility of the alloy going into solution with theberyllium. If this occurs, the window of the X-ray tube would no longerbe substantially pure beryllium, consequentl it would absorb a greateramount of the X-rays generated and one of the advantages of theinvention would be lost. Furthermore, if higher temperatures areemployed in the brazing operation, the temperature more nearlyapproaches the melting point of beryllium, which is around 1283 C.

In the practice of the invention, we have also employed as the brazingalloy, an alloy containing copper, 15% nickel, and 5% iron. This alloy,although relatively high melting (melting point around 1200 C.) gives asatisfactory joint between the beryllium and another metal, for example,cold rolled steel.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the form herein disclosed being a preferred embodiment for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. An X-ray generator comprising an evacuated casing having a portionformed with a window opening, means for generating X-rays within saidcasing for transmission therefrom through said opening, means forming asleeve on and extending outwardly of said casing and forming, thereon,an outwardly opening pocket having said window opening at the bottomthereof, and a plate of beryllium sealed at its edges on said sleeve invacuum tight fashion, said plate being positioned to permit the passageof generated X- rays therethrough.

2. An X-ray generator comprising an evacuated metal casing having aportion formed with a window opening, means for generating X-rays withinsaid casing for transmision therefrom through said opening, meansforming a. sleeve on and extending outwardly of said casing and forming,thereon, an outwardly opening pocket having said window opening at thebottom thereof, and a plate of beryllium sealed at its edges on saidsleeve in vacuum tight fashion, said plate being positioned to overliesaid window opening and permit the passage of the generated X-raystherethrough.

3. In an X-ray generator having an evacuated casing, a beryllium window,and a vacuum tight metal joint between said window and said casing, saidjoint being formed of a soldering alloy comprising a metal which in themolten state goes into solution rapidly with beryllium, alloyed with ametal, which in the molten state goes into solution slowly withberyllium, said alloy having a melting point above about 700 centigrade,but substantially below the melting point of beryllium.

4. In an X-ray generator having an evacuated casing, a beryllium window,and a vacuum tight metal joint between said window and said casing, saidjoint being formed of a soldering alloy comprising a metal which in themolten state goes into solution rapidly with beryllium, alloyed with ametal. which in the molten state goes into solution slowly withberyllium, said alloy having a melting point within the range of about700 to about 900 centigrade.

5. In an X-ray generator having an evacuated casing, a beryllium window,and a vacuum tight metal joint between said window and said casing, saidjoint being formed of an alloy of copper and silver in which therelative amount of copper present is substantially greater than theamount of copper present in the eutectic composition of said alloy.

6. In an X-ray generator having an evacuated casing, a beryllium window,and a metal joint between said window and said casing, said joint beingformed of an alloy of copper and silver in which the relative amounts ofcopper and silver are approximately equal.

'7. In an X-ray generator having an evacuated casing, a berylliumwindow, and a metal joint for joining said window to said casing, saidmetal joint being composed of an alloy of copper, nickel and iron,containing approximately 80% copper, 15% nickel, and iron.

8. A vacuum tube comprising an evacuated casing having an outwardlyextending sleeve formed thereon and providing an outwardly openingpocket having a bottom formed with a window opening communicating withthe interior of the casing, and a plate of metallic berylliumhermetically sealed in the bottom of said pocket in position overlyingsaid window opening and forming an integral part of the casing.

9. An X-ray generator comprising an evacuated casing having an outwardlyfacing seat formed on a wall thereof and provided with a window openingwithin the borders or said seat and communicating with the interior ofsaid casing, a plate comprising beryllium substantially transparent toX-rays mounted on said seat in position covering said opening, and meanscomprising solder hermetically sealing said plate on said seat aroundsaid opening, said solder comprising an alloy of copper and silver andbeing disposed outwardly of the edges of said opening, thereby avoidingsolder contamination of the portions of said plate covering saidopening.

10. An X-ray generator comprising an evacuated casing having anoutwardly facing seat formed on a wall thereof and provided with awindow opening within the borders of said seat and communicating withthe interior of said casing, a plate comprising beryllium substantiallytransparent to X-rays mounted on said seat in position covering saidopening, and means comprising solder hermetically sealing said plate onsaid seat around said opening, said solder comprising an alloy ofcopper, nickel and iron and being disposed outwardly of the edges ofsaid opening, thereby avoiding solder contamination of the portions ofsaid plate covering said opening.

ZED J. ATLEE. HOWARD BRACKNEY.

